Lubricants in commercial use today are prepared from a variety of natural and synthetic base stocks admixed with various additive packages and solvents depending upon their intended application. The base stocks typically include mineral oils, polyalphaolefins (PAO), gas-to-liquid base oils (GTL), silicone oils, phosphate esters, diesters, polyol esters, and the like.
A major trend for passenger car engine oils (PCEOs) is an overall improvement in quality as higher quality base stocks become more readily available. Typically the highest quality PCEO products are formulated with base stocks such as PAOs or GTL stocks admixed with various additive packages.
For improving fuel economy, base oil viscosity is very important. Substantial improved fuel economy (>2%) requires breakthrough in: (1) base oil volatility (2) durability and (3) friction. Friction losses occur between the moving components within the engine. Models developed to date indicate that fuel economy is heavily influenced by the lubricant properties at high shear. The base stock contributes a greater proportion of the total viscosity under high shear conditions than under low shear. Lowering base stock viscosity is likely to have the largest impact on future fuel economy gains.
Current commercial PAO fluids (e.g., SpectraSyn™ 2) based on hydrocarbon and commercial esters (e.g., 2-ethylhexyl adipate, di-2-ethylhexyl azelate, Esterex™ A32, Esterex™ A34) do not adequately allow formulation of ultra-low viscosity lubricant while still meeting API specification (e.g., Noack volatility of 15% or less). In order to formulate ultra-low viscosity lubricant for fuel economy benefit, it is desirable to have low viscosity and low volatility properties co-exist in the same base stock, for meeting volatility requirement. In addition, the base stock should also possess adequate thermal and oxidative stability at high temperature to prevent or minimize deposit formation. Good compatibility with additives commonly used in lubricant formulations (PVL, CVL, industrial lubricants), good low temperature properties, and acceptable viscosity indices are also necessary for the base stocks.
Poly-α-olefins (PAOs) are important lube base stocks with many excellent lubricant properties, including high viscosity index (VI), low volatility and are available in various viscosity range (Kv100 2-300 cSt). However, PAOs are paraffinic hydrocarbons with low polarity. This low polarity leads to low solubility and dispersancy for polar additives or sludge generated during service. To compensate for this low polarity, lube formulators usually add one or multiple polar cobase stocks. Ester or alkylated naphthalene (AN) is usually present at 1 wt. % to 50 wt. % levels in many finished lubricant formulations to increase the fluid polarity which improves the solubility of polar additives and sludge.
Therefore, there is a need for polar cobase fluids that provide appropriate solubility and dispersibility for polar additives or sludge generated during service of lubricating oils.
Future automotive and industrial trend suggest that there will be a need for advanced additive technology and synthetic base stocks with substantially better thermal and oxidative stability. This is primarily because of smaller sump sizes that will have more thermal and oxidative stresses on the lubricants. Performance requirements have become more stringent in the past 10 to 20 years and the demand for longer drain intervals has grown steadily. Also, the use of Group II, III and IV base oils is becoming more widespread. Such base oils have very little sulfur content since natural sulfur-containing antioxidants are either absent or removed during the severe refining process.
It is known that lubricant oils used in internal combustion engines and transmission of automobile engines or trucks are subjected to demanding environments during use. These environments result in the lubricant suffering oxidation catalyzed by the presence of impurities in the oil, such as iron (wear) compounds and elevated temperatures. The oxidation manifests itself by increase in acid or viscosity and deposit formation or any combination of these symptoms. These are controlled to some extent by the use of antioxidants which can extend the useful life of the lubricating oil, particularly by reducing or preventing unacceptable viscosity increases. Besides oxidation inhibition, other parameters such as rust and wear control are also important.
A major challenge in engine oil formulation is simultaneously achieving improved fuel economy while also achieving appropriate solubility and dispersibility for polar additives or sludge generated during service of lubricating oils and oxidative stability and hydrolytic stability.
Therefore, there is need for better additive and base stock technology for lubricant compositions that will meet ever more stringent requirements of lubricant users. In particular, there is a need for advanced additive technology and synthetic base stocks with improved fuel economy, solubility and dispersibility for polar additives or sludge generated during service of lubricating oils, hydrolytic stability, and oxidative stability.
The present disclosure also provides many additional advantages, which shall become apparent as described below.